Synthetic oils from alpha-olefins

ABSTRACT

FULLY HYDROGENATED NAPTHENIC HYDROCARBON LUBRICATING OILS HAVING LOW POUR POINTS, HIGH VISCOSITY INDICES AND CONTAINING AT LEAST 0.7 MOLE OF NAPHTHENE MOLECULES PER MOLE OF ISOPARAFFIN MOLECULES ARE PRODUCED BY OLIGOMERIZING C6-C12 NORMAL ALPHA-OLEFINS IN THE PRESENCE OF AN ALKALI METAL TETRAHALOALANATE CATALYST AND SUBSEQUENTLY HYDROGENATING THE RESULTING OLIGOMERIC PRODUCT.

United states Patent 3 682,823 SYNTHETIC OILS FROM ALPHA-OLEFINS George Smith, Pinole, and Johannes M. Wortel, Walnut Creek, Calif., assignors to Shell Oil Company, New

York, NY.

No Drawing. Filed June 17, 1970, Ser. No. 47,133

Int. Cl. Cm 3/12 US. Cl. 252-59 12 Claims 7 ABSTRACT OF THE DISCLOSURE Fully hydrogenated naphthenic hydrocarbon lubricating oils having low pour points, high viscosity indices and containing at least 0.7 mole of naphthene molecules per mole of isoparatfin molecules are produced by oligomerizing Cg-Cng normal alpha-olefins in the presence of an alkali metal tetrahaloalanate catalyst and subsequently hydrogenating the resulting oligomeric product.

BACKGROUND OF THE INVENTION The oligomerization of alpha-olefins to produce synthetic lubricating oils with Friedel-Crafts catalysts is well known. See, for example, French Patent 1,419,732, issued Dec. 3, 1965, to Bush et al. In general, these synthetic lubricating oils have low pour points and high viscosity indices and are useful without further treatment, particularly for low temperature lubrication. However, under high temperature lubricating conditions such lubricants are not sufliciently stable to oxidation. Although hydrogenation of the synthetic oils generally increases the oxidative stability, the pour point of the hydrogenated lubricating oil is generally substantially increased over the pour point of the lubricating oil before hydrogenation. For example, U.S. 3,113,167, issued Dec. 3, 1963, to Sauer, discloses that the hydrogenation of alpha-olefin oligomer oils produced by oligomerization of C -C alpha-olefins with a titanium halide and organoaluminum catalyst system causes the pour point of the hydrogenated oil to increase as much as 100 F. above the pour point of the oil before hydrogenation. Similarly, US. 3,149,178, issued Sept. 15, 1964, to Hamilton et al., discloses that when alphaolefin oligomer oils produced by oligomerization of alphaolefins by any of a variety of methods, e.g., thermal oligomerization, free-radical catalyzed oligomerization and Friedel-Crafts-type catalytic oligomerization, are hydrogenated, the pour points are greatly increased. Although both patents teach that the increase in pour point caused by hydrogenation can be diminished by removing all, or at least most, of the alpha-olefin dimers, either before or after hydrogenation, it would be of advantage to develop a process for producing synthetic lubricating oils of low pour points which does not require the removal of the dimer components as in many applications the presence of dimers is desirable.

SUMMARY OF THE INVENTION It has now been found that hydrogenated synthetic lubricating oils of low pour points and high viscosity indices are produced by oligomerizing 0 -0 normal alpha-ole- Patented Aug. 8, 1972 fins with alkali metal tetra-haloalanates as catalysts and subsequently hydrogenating the resulting alpha-olefin oligomers. The hydrogenated synthetic lubricating oils are characterized by low pour points, e.g., pour points at least as low as -60 F., and more often at least as low as R, which pour points are as low as the pour points of the unhydrogenated alpha-olefin oligomers. The hydrogenated lubricating oils are further characterized by a molcular composition consisting of at least 0.7 mole of alicyclic oligomers, e.g., alkyl-substituted naphthenes, per mole of isoparafiinic oligomers.

DESCRIPTION OF PREFERRED EMBODIMENTS The olefinic reactant-The olefinic reactants useful in the preparation of the synthetic oils are normal alpha-olefins of from 6 to 12 carbon atoms, i.e., l-hexene, l-heptene, l-octene, l-nonene, l-decene, l-undecene and 1- dodecene. A single alpha-olefin or a mixture thereof is suitably employed. Generally, however, synthetic oils of superior properties are obtained with Cg-Cm alpha-olefins or with mixtures of alpha-olefins having an average chain length of about 8 to 10. Suitable mixtures of alpha-olefins are C -C alpha-olefin mixtures obtained by Zieglertype polymerization of ethylene. A particularly preferred alpha-olefin mixture comprises a mixture of 25% mole l-hexene, 25% mole l-octene and 50% mole l-decene.

The Catalyst-The alkali metal tetrahaloalanate catalysts have the general formula MAlX, wherein M is an alkali metal of atomic number from 3 to 55, i.e., Li, Na, K, Rb or Cs, and X is a halogen of atomic number from 9 to 53, i.e., F, Cl, Br or I. Some examples of suitable alkali metal tetrahaloalanates are: LiAlF KAIF CsAlF LiAlCl NaAlC1 KAlCl RbAlCl LiAlBr NaAlBr CsAlBr LiAlI KAlI and RbAlL Other suitable alkali metal tetrahaloalanates are those containing more than one halogen such as NaAlCl Br and LiAlBr Cl. Preferred alkali metal tetrahaloalanates are those wherein the alkali metal is lithium, sodium or potassium and the halogen is a middle halogen, i.e., chlorine or bromine. Particularly preferred is lithium tetrachloroalanate.

The alkali metal tetrahaloalanate catalysts are prepared by a variety of methods. In one modification, the alkali metal tetrahaloalanates are prepared by melting together essentially stoichiometric quantities of an alkali metal halide and an aluminum trihalide, e.g., NaCl and AlCl LiBr and AlBr or KCl and AlBr Alternatively, the alkali metal halide and aluminum trihalide, components are formed as a slurry in a liquid organic medium. Suitable organic media include aliphatic hydrocarbons and halohydrocarbons free from unsaturation such as dichloromethane, dibromoethane, hexane, heptane, isooctane, decane, and cyclohexane. Subsequent to the contacting of the alkali metal and aluminum trihalide components, the resulting alkali metal tetrahaloalanate catalyst is separated from the solvent, if desired, by conventional techniques, such as filtration and decantation. In a preferred modification of the process, however, a slurry of the catalyst in the organic medium is directly employed in the alpha-olefin oligomerization process wherein the presence of a reaction solvent is desired.

The amount of oligomerization catalyst employed in the oligomerization process is not critical. Generally, molar ratios of alkali metal tetrahaloalanate to alpha-olefin reactant of from about 1:5 to 1:500 are satisfactory with molar ratios of about 1 :15 to 1:50 being preferred.

Reaction conditions-The oligomerization process is conducted by contacting in the liquid phase the alphaolefin reactant, the catalyst and a reaction solvent or diluent which is capable of dissolving the alpha-olefin reactant, is liquid at reaction temperature and pressure and is inert to the reactants and product produced therefrom. Suitable diluents include alkanes such as pentane, hexane, heptane, isooetane, and decane; cycloalkanes such as cyclopentane and cyclohexane; and halogenated alkaues such as methyl and ethyl chlorides, methyl and ethyl bromides. Preferred diluents are alkanes of from 5 to 8 carbon atoms, particularly hexane and octane. In some modifications of the oligomerization process, a portion of the alpha-olefin reactant and the oligomer product suitably serves as reaction diluent. The use of a diluent is generally preferred, however, and when a diluent is utilized amounts up to about four moles of diluent per mole of alpha-olefin are satisfactory. The process is suitably conducted in an inert reaction environment so that the presence of reactive materials such as water and oxygen is desirably avoided. Reaction conditions are therefore substantially anhydrous and substantially oxygenfree.

The precise method of establishing alpha-olefin catalyst contact is not critical. In one modification, the alphaolefin reactant, catalyst and diluent are charged to an autoclave or similar pressure reactor, and the reaction mixture is maintained with agitation at reaction temperature and pressure for the desired reaction period. In. another modification, one reaction component is added to the other component in increments, as by adding the catalyst to the solution of the alpha-olefin and diluent. By any modification, the process is most efiiciently conductedat elevated temperature and pressure. In general, temperatures varying from about 50 C. to 200 C. are satisfactory with temperatures from about 100 C. to 150 C. being preferred. Suitable reaction pressures are those which serve to maintain the reaction mixture substantially in the liquid phase. Reaction pressures from about 1 atmosphere to about 50 atmospheres in general are satisfactory although autogenous pressure, that is, the pressure generated by the reaction mixture when maintained at reaction temperature in a sealed reaction system is'preferred. The contact time depends in part upon the reaction condition and the particular catalyst employed, but is usually between /2 hour to 20 hours and preferably between 1 hour to 4 hours.

At the conclusion of the oligomerization reaction, the catalyst is recovered from the alpha-olefin oligomeric mixture for re-use. The oligomeric product mixture is generally washed with a caustic solution to destroy any residual catalyst, water washed and then subjected to a flash distillation to recover the diluent.

-In order to obtain the novel and improved synthetic oils of the invention, the alpha-olefin oligomeric product is hydrogenated by any more or less conventional procedure. Suitable catalysts include metallic catalysts such as Pt, Pd, or Ni, and metal oxides such as platinum oxide and copper chromite. The hydrogenation catalysts are employed as the unsupported materials or as supported materials on carriers such as silica and alumina. Preferred hydrogenation catalysts are nickel catalysts, especially commercial Raney nickel and nickel on kieselguhr.

The hydrogenation process is conducted at elevated temperature and pressure. Suitable reaction temperatures vary from 50 C. to 200 C., the optimum temperature depending in part upon the particular catalyst employed. Hydrogen pressures from about 10 atmospheres to about 200 atmospheres are satisfactory but hydrogen pressures. from about 30 to 100 atmospheres are preferred.

Prior to hydrogenation, the alpha-olefin oligomeric product contains a residual amount of ethylene unsaturation due to the presence of small amounts of highly substituted internal olefins. The presence of this residual unsaturation can be detected by Raman-Laser spectroscopy due to the existence of a strong Raman band that arises from the C=C stretching vibration in the 1640-1680 cm. region. Consequently, in order to obtain a synthetic oil of good thermal and oxidative stability, it is essential that the alpha-olefin oligomeric product be hydrogenated to remove the residual unsaturation.

The synthetic oil product.The oligomerization of the alhpa-olefin reactant and the subsequent hydrogenation of the resulting alpha-olefin oligomers produces a synthetic lubricating oil consisting of saturated O -C oligomers, generally dimers, trimers, tetramers, pentamers, hexamers and heptamers. The oligomers are characterized by a unique combination of alicyclic oligomers and isoparaffinic oligomers. The alicyclic oligomers consist essentially of 5 and 6 membered naphthenes substiuted with several isoalkyl side chains. Most of the naphthenic oligomers contain a single naphthenic ring although a small amount, usually about 0.1 to 0.2 mole per mole of total naphthenic oligomers, contain two naphthenic rings. -In general, the synthetic lubricating oil consists of at least 0.7 mole of naphthenic oligomers, preferably of at least 0.8 mole, and most preferably the molar ratio of naphthenic oligomers to isoparafiinic oligomers is from about 0.85:1 to 1:1. The average molecular weight of the synthetic lubricating oil is usuallyabout 350 to 700, but preferably is about 450 to 6 00.

The hydrogenated synthetic lubricating oil is further characterized by a unique combination of both excellent high temperatures and low temperature properties as refiected particularly in low pour points and high viscosity indices. In general, the viscosity index of the hydrogenated alpha-olefin oligomers is at least 110, and in most 1nstances, is at least 125. The pour points are generally no higher than -60 F. and preferably no higher than --70 F. Although it is not known with certainty, it is considered likely that low pour points of the alpha-olefin oligomers, even after hydrogenation, is due to the novel ratio of isoparafiinic to naphthenic oligomers in the lubrieating oil. For eoarnple, it has been found that alphaolefin oligomers produced with a di-tert-butyl peroxide catalyst, as taught in US. 3,149,178, contains less than 21% naphthenes. As heretofore indicated, the pour points of such alpha-olefin oligomers are increased by as much as 50 F. to F. after hydrogenation.

Examples I-VIII A number of experiments were carried out on the oligomerization of a variety of alpha-olefins with LiAlCl as catalyst.

The reaction temperature was C., reaction times ranged from 1.5 hours to 4 hours and n-hexane or noctane was utilized as the reaction solvent. The molar ratio of LiAlCl to alpha-olefin feed was 20:1. Each experiment was conducted by adding the olefin feed to a slurry of the catalyst in the reaction solvent. The catalyst was then removed from the reaction mixture, the oligomeric product mixture was washed once with 2.5% so dium carbonate or sodium hydroxide and twice with water to remove all traces of the catalyst. The solvent and unreacted olefin feed were then removed by rotary evaporation at elevated temperature and reduced pressure to give the oil product. The oil product was then hydrogenated with 5% wt. Raney nickel at 1500 p.s.i.g. hydrogen pres sure for 8 hours at C. The hydrogenated oil was then topped by distillation to remove dimers at elevated temperatures (97-200 C., stillhead) and reduced pressures (0.07 to 0.5 mm. of Hg).

The alpha-olefin feed employed and the properties of the unhydrogenated and hydrogenated oil products are provided in Table I.

TABLE I Emmnle I II III IV V VI VII VIII 257 m. 00 33.3% m. C 257 m. 0.50% m. o. 20% m.{ 0 v ..:'."..":.r.'':.'..'..'..' C C 0 Ca 259' In. Us 33.37 m. Ca 507 m. Alpha-olefin feed a a m C8 50% on 80% 61050;}; m. 01033-3 7 5 111. C12 25% 111. Mean chain length 6 8 10 7 9. 6 8. 5 8 8. 5 Oil rjgopertieszt o F U hydrbgenated oil -70 -70 --70 70 -70 -70 -70 -70 Hydrogenated oil:

B fore to in dimers -70 -70 70 70 -70 70 -65 70 Ai ter topgi hg dimers 70 -70 70 70 70 -70 -45 -70 ViscEoIsitgrindexi: d u

y ogena e o Before to in dimers- 110 125 135 116 131 133 140 130 After topgi ng dimers 103 131 125 116 121 122 122 128 Kinematic viscosity, cs.:

Hydrogenaged o il: dim

-io ia at 22, 950 14, 740 26, 890 8, 500 8, 060 15, 800 36, 970 100 F- 27. 8 49. 7 42. 7 49. 1 31. 8 30. 4 44. S 68. 3 210 F 4. 91 7. 67 6. 99 7. 18 5. 67 5. 54 7. 37 9. 54 1Z8 j 63,400 40, 200 41,420 42,500 49,020 30,300 70,950 47, 960 00.2 .2 72. 4 60.2 71. 9 57. 3 90. s 70. 4 7. 82 9. 93 9. 79 8. 24 9. 49 8. 11. 20 10. 24

Example IX Example XI A sample of KAlCl was prepared by heat 50 g of KCl 40 of A Sample of L1A1C14 was Prepared by heatmg g and 80 g. of AlCl in 432 g. of n-octane with vigorous LiCl and 114 g. of AlCl at 200 C. and subsequently cooling and dispersing the resulting LiAlCL; in 400 ml. of n-hexane. The slurry of LiAlCl in n-hexane and a mixture of 360 g. of l-hexene, 480 g. of l-octene and 1200 g. of l-decene were then continuously added over a period of 90 minutes to 616 g. of n-hexane contained in an autoclave maintained at 125 C. At the end of the 90 minute addition period, the reaction mixture was maintained at 125 C. for an additional 20 minutes. The reaction mixture was then cooled, the oligomeric product mixture was separated from the LiAlCl catalyst and washed once with 2.5% NaOH solution and twice with water at 74 C.

The oligomeric product mixture was then hydrogenated with a commercial 44% wt. Ni-on-kieselguhr catalyst at 200 C. and 1500 p.s.i.g. hydrogen pressure for 8 hours. The n-hexane solvent and unreacted olefins were removed at atmospheric pressure in a wiped-film-evaporator at 100 C. The resulting oil was then topped to remove dimers at reduced pressure (5 mm. of Hg) and a temperature of 240 C. in the same wiped-film-evaporation in a second pass.

The unhydrogenated oil (after removal of n-hexane solvent and olefin monomers) and the hydrogenated oil (before topping of dimers and after topping of dimers) had properties set forth in Table II under Run 1. The isoparafi'in and naphthene contents of the oil (after hydrogenation) were determined by high resolution mass spectroscopy.

Example X A sample of NaAlCl. was prepared by heating 39 g. of NaCl and 80 g. of A101 in 432 g. of n-octane with vigorous stirring in an autoclave maintained at 150 C. for 1 hour. A mixture of 376 g. of l-hexene, 506 g. of 1- octene and 1202 g. of l-decene was then added continuously over a period of 115 minutes to the autoclave maintained at 150 C. At the end of the 115 minute period, the autoclave was maintained at 150 C. for an additional 20 minutes. The reaction mixture was then cooled, the catalyst slurry removed, the oligomeric product mixture was washed with Water, dried and filtered. The n-octene solvent and unreactcd olefin monomers were then removed with a rotary evaporator at 95-100 C. and at a reduced pressure. The resulting oil produce was then hydrogenated with 5% Raney Ni at 1500 p.s.i.g. hydrogen pressure for 8 hours at 150 C. The hydrogenated oil was then topped by distillation to remove dimers at 148 C. (stillhead) and 0.5 mm. of Hg.

The unhydrogenated oil and the hydrogenated oil had the properties set forth in Table II under the column designated as Run 2.

stirring in an autoclave maintained at 150 C. for 1 hour.

A mixture of 376 g. of l-hexene, 506 g. of l-octene and 1202 g. of l-decene was then added continuously over a period of minutes to the autoclave maintained at 150 C. At the end of the 90 minute period, the autoclave was maintained at 150 C. for an additional 20 minutes. The reaction mixture was then cooled, the catalyst slurry was removed, the oligomeric product mixture was washed with water and dried. The n-octane solvent and nnreacted olefin monomers were then removed with a rotary evaporator. The resulting oil product was then hydrogenated with 5% Raney Ni at 1500 p.s.i.g. hydrogen ressure for 8 hours at 150 C. The hydrogenated oil was then topped by distillation to remove dimers at 150 C. (stillhead) and 0.5 mm. of Hg.

The unhydrogenated oil and the hydrogenated oil had the properties set forth in Table '11 under the column designated as Run 3.

Example XII A mixture of 30.7 g. of di-tert-butyl peroxide and 588 g. of l-decene were heated in an autoclave at 150 C. for 5 hours. The resulting oil product was cooled, distilled to remove unconverted l-decene, and then hydrogenated with 5% wt. Raney Ni at 150 C. for 3 hours at 1500 p.s.i.g. hydrogen. The resulting hydrogenated oil was then topped by distillation to remove dimers at 193 C. (stillhead) and 0.4 mm. of Hg.

The unhydrogenated oil (after removal of l-decene) and the hydrogenated oil had the properties set forth in Table II under Run 4.

TABLE 11 Run Number.. 1 2 3 Di-tertbutyl Catalyst LiAlOlr N aAlCl KAlClr peroxide Oil properties:

Isoparatfin content- 51 55 48 79 Naphthene content- 49 45 52 21 Ratio naphthene/ isoparaffin 0. 96 0. 82 1.08 0.27 Pour points, F.:

Unhydrogenated oil -70 -70 70 -60 Hydrogenated oil:

Before topping dimers -70 70 -70 +35 After topping dimers 70 -70 55 -50 Viscosity index:

Hydrogenated oil:

Before topping dimer 120 156 After topping dimer 126 152 119 143 7 Example X lII To illustrate the superior thermal and oxidative stability of the hydrogenated lubricating oil of the invention, the unhydrogenated (unsaturated) liquid oil of Example IX, Run 1 and the hydrogenated oil of Example IX, Run 1, (before topping of dimers) were submitted to oxidation by air at 350 F. for 22 hours. The color, acidity and evaporative loss for each oil is provided in Table III.

TABLE III Unsaturated Hydrogenated Color (Gardner scale)-.- 3-4 1 Acidity, meg/1000 g 0. 25 l 0. 07 Evaporative loss, percent w 12. 8 12. 8

' Detection limit.

Example XIV The properties of an equal molar blend of the hydrogenated C C and C alpha-olefin oligomers (before topping of dimers) prepared in Examples I, II and HI, respectively, were measured and tabulated below in Table IV under the column designated Blend of Homo-Oligomers. For comparison, the properties of an oligomeric oil produced from a mixed C C and C alpha-olefin feed (Example VII) are also tabulated in Table IV under the column designated Co-oligomers.

TABLE IV Blend of homooligomcrs Co-oligomer g gs/Ci molar rgtio 1/1/1 1/1/1 ma viseosi cs.:

8 t 21 o Fm"?! 7.5 7.4 At 100 F. 49. 6 44. 8 At -40 F.-- 22, 700 15, 800 Viscosity index 125 140 Pour point, F -65 70 Evaporative loss, percent wt 16. 2 15. 7

We claim as our invention:

1. A hydrogenated high-naphthenic content dimercontaining hydrocarbon synthetic lubricating oil consisting essentially of C to C naphthenic and isoparaflinic oligomers of a C -C normal alpha-olefin, said lubricating oil having all the following properties: a maximum pour point of about F., a minimum viscosity index of about 110 and a molar ratio of naphthenic oligomers to isoparafiinic oligomers of at least 0.7:1.

2. The lubricating oil of claim 1 wherein the alphaolcfin is a C C alpha-olefin or a mixture of alphaolefins with mean chain length of about 8 to 10.

3. The lubricating oil of claim 2 wherein the maximum pour point is F., the minimum viscosity index is 125 and the average molecular weight is 450 to 600.

4. The lubricating oil of claim 3 wherein the alphaolefins are a mixture of 25% m. l-hexene, 25% m. 1- octene and 50% m. l-decene.

5. The lubricating oil of claim 4 wherein the molar ratio of naphthenic oligomers to isoparaffinic oligomers is from about 0.85: 1 to 1: 1.

6. A process of producing a fully saturated high-naphthenic content hydrocarbon synthetic lubricating oil consisting essentially of naphthenic and iso paraflinic C -C oligomers with a molar ratio of naphthenic oligomers to isoparaflinic oligomers of at least 0.7 1, having a viscosity index of at least and a maximum pour point of about -60 F. which comprises:

(a) oligomerizing a C to C normal alpha-olefin to an oligomeric product mixture of C to C oligomers in the presence of an alkali metal tetrahaloalanate catalyst, the molar ratio of catalyst to alphaolefin being about 1:5 to 1:500, at a temperature of 50 C. to 200 C., and

(b) hydrogenating the oligomeric product mixture to produce the lubricating oil product.

7. The process of claim '6 wherein the alkali metal is Na, K or Li.

8. The process of claim 7 wherein the halogen of the tetrahaloalanate catalyst is chlorine or bromine.

9. The process of claim 8 wherein the alpha-olefin is a C -C alpha-olefin or a mixture of alpha-olefins with mean chain length of about 8 to 10.

10. The process of claim 9 wherein the alpha-olefin mixture is 25% mole l-hexene, 25% m. l-octene and 50% mole l-decene.

11. The process of claim 9 wherein the lubricating oil has a maximum pour point of about --70 F. and a viscosity index of at least 125.

12. The process of claim 9 wherein the catalyst is lithium tetrachloroalanate.

References Cited UNITED STATES PATENTS 3,113,167 12/1963 Sauer 260-683.15 D 3,149,178 9/1964 Hamilton et al. 260683.9 3,349,148 10/1967 Bush 260683.15 B

HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

